Howdy. Before I get into the meat of the guide, I'll explain how I got into playing Cassiopeia, often considered one of the most difficult champions in the game. Some time a few months ago, Cassiopeia was free, piquing my interest. I knew that she was hard, but I had seen a good friend of mine (iluswirl) playing her and facerolling. I asked him for his build, played a few games, and enjoyed playing her so much I soon bought her. In fact, this guide is in fact based on his build. She takes practice to reliably do well, but don't get discouraged. Once you become skilled with her, she is dazzlingly good.

Also, this is my first ever guide I've written for mobafire; one that I have actually been sitting on for a few months until I felt it was completely ready for a release. Be as critical as you please, I'm a shameless perfectionist.

This is what I use, but feel free to change these around as you like. In the Mark slot I have magic penetration runes, which will help your poison do even more. The mana regen seals will help you in laning phase, while the flat AP glyphs and quints are obvious choices for any AP carry. I prefer AP quints over magic penetration quints myself, but you can choose as you will.

Deadly Cadence [passive]:
After casting a spell, any subsequent spellcasts will cost 10% less for 5 seconds. This ability stacks up to 5 times.
This is your passive ability. It's what lets you spam your abilities with the best of them midgame. This isn't one of those passives in which you need to keep an eye on the effect icon--this works quietly in the background.



Noxious Blast [Q]:
Cassiopeia blasts an area with a delayed high damaging poison, dealing magic damage over 3 seconds and granting her movement speed for 2 seconds if she hits a champion.
Cooldown: 3 seconds
Cost: 35 / 45 / 55 / 65 / 75 Mana
Magic Damage: 75 / 115 / 155 / 195 / 235 (+0.9 per Ability Power)
Movement Speed: 15 / 17.5 / 20 / 22.5 / 25 %

A great spell, and your bread and butter. After a brief delay, this spell infects every enemy unit (save for buildings, of course) in a circular area with a fairly strong poison. In early laning phase, you can destroy the enemy midlaner if they aren't careful about dodging this, so keep on harassing! I like to throw this into a group of minions as the enemy champion approaches, helping you get some farm and whittling down their health. And remember, because you get a two second speed buff from hitting a champion with this ability, you can check bushes with this ability: if you receive the buff, then there's an enemy champion in the bush and you should be careful.



Miasma [W]:
Cassiopeia releases a growing cloud of poison that lasts for 7 seconds. Any enemy that passes through it is poisoned for 2 seconds, dealing magic damage each second and slowing them. Continual exposure renews this poison.
Cooldown: 9 seconds
Cost: 70 / 80 / 90 / 100 / 110 Mana
Magic Damage: 25 / 35 / 45 / 55 / 65 (+0.15 per Ability Power)
Slow: 15 / 20 / 25 / 30 / 35 %

Your primary farming spell, which doubles as a good zoning slow when you have your Rylai's. Throw this into the middle of a teamfight, and watch the carries scatter. As the incoming wave approaches, cast this spell ahead a bit, estimating where the two minion waves will meet (friendly and enemy) so that the poison will spread through hopefully both lines of minions. In terms of damage, it is far inferior to Noxious Blast, so don't rely on it for dealing damage to enemies that aren't minions.



Twin Fang [E]:
Cassiopeia deals magic damage to her target. If the target is poisoned then Twin Fang's cooldown is reduced to .5 seconds.
Cooldown: 5 (.5 if poisoned) seconds
Cost: 50 / 60 / 70 / 80 / 90 Mana
Magic Damage: 60 / 95 / 130 / 165 / 200 (+0.45 per Ability Power)

This is the skill you want to spam really hard on poisoned enemies. It makes a great two-part harass in laning phase, first casting Noxious Blast on an enemy champ then Twin Fang. Be warned, however, it can be expensive mana-wise. As well, remember that this ability does not have a very large range, so you'll need to be getting up close and personal to use this. Be careful to not expose yourself to the line of fire of the carries when trying to combo this ability with your Q or W. However, it's still a solid ability to harass enemies with. And remember: it's a waste of mana to cast this on an enemy that's not poisoned. The strength of this spell lies in the fact that it's great for spamming, not that it deals insane damage with one hit.



Petrifying Gaze [R, Ult]:
Cassiopeia deals magic damage to all enemies in front of her. Enemies facing her are stunned for 2 seconds while enemies facing away are slowed.
Cooldown: 120 seconds
Cost: 120 / 160 / 200 Mana
Magic Damage: 150 / 275 / 400 (+0.6 per Ability Power)
Slow: 40 / 50 / 60 %
Stun: 2 Seconds

This is what separates the good Cassiopeia players from the bad. This is one of the hardest ults to use well in the game, hands down. It's a risky ability, as you will need to go up to the front of a teamfight to use this. However, when done right, it can turn it around entirely. However, you need to have good timing and trick them: most good players will know to turn around so they will simply be slowed. To lift from Furber's excellent guide,
"This ult is good for turning a push around. When your team is retreating from their team, look for an opportunity to turn back quickly and ult their team. If done correctly, the result will be similar to an Amumu ult. Your team can turn around and beat on the enemies for 2 full seconds. This should be enough to gain the advantage in the team fight, and hopefully you will win."

As well, don't forget that you can use this ultimate for escape. Try and chase your pursuers into a tower, then stun them within range of it, allowing them to soak up your poison and some tower shots. If a turret's not on hand, stun them then Flash over a wall, and try to get lost within the bushes. On the other hand, you can Flash towards the fleeing enemy, have your tank try and taunt them forward to face you, then pop your ult on them.

Ignite: Goes hand in hand with your DoT damage. After casting your Q+W combo, deny them the chance to escape by putting this spell on them quickly. Don't be shy about towerdiving, putting this spell on him, then using Flash to escape.

Flash: A simply excellent spell that can be used for both offensive and defensive purposes. A great spell to escape ganks, and to atttack. You should almost always have this spell on you.

Ghost: Can be used as an alternative to Flash, this will help you chase your prey or to escape. Personally, I don't recommend it, but if you like it better, then go ahead.

Exhaust: A good spell for both escaping and preventing an enemy from escaping. Can be used as an alternative for Ignite.

Teleport: Can be handy as Cassiopeia isn't very fast, but its use is still limited for a midlaner.

Cleanse: A helpful spell, as Cassiopeia is very easily focused down if she isn't careful. However, it doesn't guarantee an escape so it requires good judgement of when to use it.

First, get a Doran's Ring. After coming back to base the first time, try and have enough to buy both basic boots and another of these babies, as well as two health potions if you have enough. To quote jhoihoi's great Malevolent Morgana guide, these are the reasons why stacking Doran's is great:
// Effective early game.
// Incredibly cost efficient
// More lane presence
// Situationally effective
// Survivability - cushion against harassment but not a counter

After getting your boots and the two Doran's (if you only have enough for one get the ring), start building your Rod of Ages by getting a Catalyst The Protector. Remember, the sooner you get your Rod of Ages, the more it will benefit you. It takes ten minutes for your Rod to become fully charged, but once it gets there you will have become quite a bit less squishy, but you can still get focused down. After getting the Rod of Ages, get your Sorcerer's Shoes and continue with starting your Rylai's Crystal Scepter if you have enough money to. By this time the game should be somewhere around the 25 minute mark. After finishing your Rylai's, the game will often end just as you get your Morello, if things have been going your way. After your Rylai's, grab a Hextech Revolver, or a Banshee's Veil if you're getting focused down a lot. After the Revolver, get your Morello's. In the off case that the game does continue for a while, get a Rabadon's Deathcap and then finish the Hextech with a Will of the Ancients.

As the game begins, grab your first Doran's Ring and head out to mid. Unless there's some insane burst caster on your team that will dominate, you should always be going mid (unless you're brave enough to jungle Cass). To quote Skisquirrel's guide, "If you're good at aiming, you will win almost any harass war, and Twin Fangs effectively counters most mids who commit early." Harass with Noxious Blast, and use Twin Fang on overeager midlaners. By the time you have enough to buy basic boots and your next Doran's Ring, you should have already gotten a kill, or at least forced the enemy champion to recall for health and mana. Remember, don't be afraid about using Ignite, as it can often ensure a kill for you.

After getting your boots and the second Doran's Ring, start on your Rod of Ages, or a Mejai's Soulstealer if you are feeling confident that you can snowball your way to the top of the scoreboard. I personally always get a Rod of Ages, because it gets you quite a few good things once it's charged. Around the time you get enough for your Rod of Ages, at least one tower has likely been dropped insofar. If it was you who killed the tower, head back to your friendly tower and recall. Finish your boots, and start on your Rylai's if you have enough gold.

On Ganks:

Be careful of getting ganked by the enemy jungler, or anyone in fact. Even if your teammates call MIA reliably, still keep an eye on the minimap. Knowledge is power, and to that end, place wards in both of the straight bushes to the side of mid-lane if you don't have a jungler or a support that isn't putting them out. If you do not have wards placed, look for the danger signs. If the enemy champion is letting you push your lane freely, then there is likely a ganker coming. You do not need to hug your tower, but remain near it, at least close enough to Flash into its range. If you're feeling cheeky and they chase you into your tower's range, swivel around and use your ult on them, locking them within your tower's range and your poison. I've made an enemy gank backfire this way several times, it's quite a bit of fun.

By this time, assuming the game has gone in your team's favor, you should have one or two kills. Return to your lane, and continue pushing, taking blue buff once your jungler doesn't need it. Continue building your Rylai's. After finishing it, buy a Hextech Revolver and then a Morello's Evil Tome. As stated in the items section, by the time you get to your Morello's, the game will often be all but finished (if you need more sustain, buy a Will of the Ancients instead). In the off chance that the game does stretch on, build a Rabadon's Deathcap. Presuming you got a Morello's, finish your Will of the Ancients. Alternately, if you did not get a Morello's, instead skipping to a WotF, take your pick of the AP items. I would recommend getting a Zhonya's Hourglass, in case things get sticky, and one of the magic-penetration items ( Abyssal Mask, Void Staff), or whatever you feel would complement your role in your current game the best.

Teamfights:

Your role in teamfights is to do as much damage as you can, while punishing the enemy team for being out of position. In particular, you excel at taking down grouped champions, with your ultimate, Petrifying Gaze, and your Noxious Blast. Work with your team to victory, and keep in mind that you are a squishy, and more or less a glass cannon. You can do insane damage to the unwary opponent, but you can't take it either, so don't go to the front of the teamfight unless you plan on using your ult. Harass not unlike you would in laning phase, just with less concern for mana.

Throw your Q and your E on appropriate targets, and use Miasma to slow them when you have a Rylai's Crystal Scepter. Even without, it can be helpful for forcing enemies out of an area. For more details about each ability, see the ability section.

Change Log:

11-5-11: This guide was released. [v1]
12-20-11: Remembered that I had this and realized why this wouldn't show up, fixed that and updated a few things in the wake of the Season 2 changes. [v2]

To-do List:

-Write an alternate build, or at the least update the Items section with alternate items.
-Polish the guide visually a bit
-Add more detail to certain sections.

Thanks To:

iluswirl, for getting me started on Cassiopeia.
Furber, for writing There's A Snake in my Boot, a great Cass guide that I used for reference while writing this.
illke994, who wrote another fantastic guide I used for reference while putting this together. http://www.mobafire.com/league-of-legends/build/introducing-cassiopeia-to-competitive-scene-152382
jhoijhoi, for her helpful manual on making a good guide.
You, for reading this far.